Method and apparatus for processing video data

ABSTRACT

A method for signalling an intra chroma prediction mode and a method for implementing the signalled intra chroma prediction mode, the intra chroma prediction mode taking an intropolation of previously predicted luma samples from neighboring blocks of video data to attain an intra chroma prediction of a current chroma prediction unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/083,896, filed Apr. 11, 2011, now allowed, which claims the benefitof U.S. Provisional Patent Application No. 61/322,292 filed on Apr. 9,2010; U.S. Provisional Patent Application No. 61/322,293 filed on Apr.9, 2010; U.S. Provisional Patent Application No. 61/453,955 filed onMar. 17, 2011; U.S. Provisional Patent Application No. 61/453,981 filedon Mar. 18, 2011; U.S. Provisional Patent Application No. 61/454,565filed on Mar. 20, 2011; and U.S. Provisional Patent Application No.61/454,586 filed on Mar. 21, 2011, all of which are hereby incorporatedby reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for performingintra prediction mode decoding on digital video data that has beenencoded using an intra prediction mode. The present invention alsorelates to a method and apparatus for signaling the proper intraprediction mode to a decoding unit.

2. Discussion of the Related Art

Generally, there are two methods for accomplishing video compressionencoding in order to eliminate temporal and spatial redundancy.Eliminating temporal and spatial redundancy is an important requirementto increase a compression ratio of a video signal in order to decreasean overall size of a video data transmission.

An inter prediction encoding method is able to predict a current videodata block based on similar regions found on a previously encodedpicture that temporally precedes a current picture that includes thecurrent video data block. And an intra prediction encoding method isable to predict a current video data block based on previously encodedblocks that are adjacent to the current video data block and within asame picture. The inter prediction method is referred to as a temporalprediction method, and the intra prediction method is referred to as aspatial prediction method.

Video data comprised of inter predicted and intra predicted video datapictures are transmitted to a receiver and then decoded to reproduce thevideo data. A decoding unit must perform the proper prediction modeprocessing in order to reconstruct the received video data.

Pertaining to the intra prediction method of encoding, there existsvarious modes for accomplishing the spatial prediction that defines theintra prediction method. And within both the inter and intra predictionmethods, the prediction for a luminance (luma) sample is handledseparately from a prediction of a chrominance (chroma) sample. Luminancecan be defined as the brightness of an image, and chrominance can bedefined as a representation of color difference within an image.Although both luma and chroma are important components in any pictureimage, due to the human visual system being more sensitive to variancesin luminance as compared to variances in chrominance, prediction modeshave generally been more concerned with luma prediction modes comparedto chroma prediction modes.

Accordingly, none of the currently recognized chroma prediction modescontemplate reconstructing a chroma sample by utilizing a linearcombination of interpolated luma samples. By taking advantage of theinterpolation of luma samples, where the luma samples have beenpreviously reconstructed, a new mode for efficiently predicting thechroma sample can be achieved.

There also exists a need to conserve a number of codeword bits whentransmitting binary codewords related to information transmitted alongwith video data as part of the overall video data signal. Whentransmitting large amounts of video data, it becomes even more importantto conserve the number of codeword bits that are transmitted along withthe video data in order to conserve the number of overall bits beingtransmitted. This allows for a more efficient compression of the videodata signal as a whole.

SUMMARY OF THE INVENTION

It is an object of the present invention to introduce a method andapparatus for prediction processing an intra chroma sample that is ableto reconstruct a chroma sample by using a linear combination ofpreviously reconstructed luma samples that have been interpolated.

It is also an object of the present invention to provide a moreefficient method and apparatus for signaling and identifying a propercurrent prediction mode by relying on prediction mode informationpreviously identified. By relying on previously identified predictionmode information to determine a proper current prediction mode, areduction in overall codeword bits that need to be transmitted by anencoding unit may be accomplished.

The present invention provides a new model for performing chromaprediction on a current chroma sample that is based on a linearcombination of previously reconstructed luma samples that have beeninterpolated. This new model for performing chroma prediction alsoutilizes previously reconstructed luma samples that have beeninterpolated and previously reconstructed chroma samples, where thesesamples are taken from blocks that neighbor the current chroma sample.By utilizing a linear combination of previously reconstructed lumasamples from the same block as the current chroma sample, previouslyreconstructed luma samples that have been interpolated and are from ablock neighboring the current chroma sample, and previouslyreconstructed chroma samples that are from a block neighboring thecurrent chroma sample, a higher prediction accuracy for the chromasample can be achieved.

The present invention also accomplishes a reduction in overall codewordbits that need to be transmitted, thus reducing an overall transmissionof bits in a bitstream. This is accomplished by making informationtransmitted later in time dependent on information transmitted prior intime when possible.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a block diagram of an encoding unit according to the presentinvention;

FIG. 2 is an illustrative view of encoded video data;

FIG. 3 is a block diagram of a decoding unit according to the presentinvention;

FIGS. 4A to 4D illustrate available intra prediction modes according tosome embodiments of the present invention;

FIG. 5 illustrates a video data picture partitioned into slice units;

FIG. 6 is a close up view of an area specified from FIG. 5;

FIG. 7 is a close up view of an area specified from FIG. 6;

FIG. 8 illustrates the result of an interpolation process according to apreferred embodiment of the present invention;

FIG. 9 illustrates the result of an interpolation process according toanother embodiment of the present invention;

FIG. 10 illustrates the result of an interpolation process according toanother embodiment of the present invention;

FIG. 11A is a table of available luma prediction modes according to apreferred embodiment of the present invention;

FIG. 11B is a table of available luma prediction modes according toanother embodiment of the present invention;

FIG. 12 is a graphical illustration of available prediction modesaccording to some of the embodiments in the present invention;

FIG. 13 is a block diagram of a prediction processing unit according toa preferred embodiment of the present invention;

FIG. 14A is a table mapping the relationship between luma predictionmode information and chroma prediction mode information;

FIG. 14B is a binary codeword representation of the table in FIG. 14;

FIG. 15 is a table comparing the numerical value for intra chromaprediction modes against their binary bit codeword value;

FIG. 16 is a flowchart illustrating the transmission of intra predictionmode values;

FIG. 17 is a flowchart illustrating a signaling method for identifying aproper intra chroma prediction mode according to an embodiment of thepresent invention;

FIG. 18 is a flowchart illustrating a signaling method for identifying aproper intra chroma prediction mode according to another embodiment ofthe present invention;

FIG. 19 is a flowchart illustrating a signaling method for identifying aproper intra chroma prediction mode according to another embodiment ofthe present invention;

FIG. 20 illustrates a method for transmitting transform unit sizeinformation according to the present invention;

FIG. 21 illustrates a method for transmitting transform unit sizeinformation according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a methodfor decoding digital video data includes receiving a sequence ofpictures that comprise the video data, each picture of video data beingcomprised of at least one slice, and each slice being comprised of atleast one treeblock. Each treeblock being partitioned into a number ofprediction units, and performing a prediction on each prediction unitaccording to a corresponding prediction mode in order to reconstruct thevideo data. The corresponding prediction mode should be the sameprediction mode used for encoding the prediction unit prior totransmission.

According to the present invention, prediction mode type information isreceived along with the video data for identifying a prediction mode ofeach prediction unit of the video data. The prediction mode typeinformation distinguishes between inter prediction modes and intraprediction modes. The prediction mode type information alsodistinguishes between prediction modes corresponding to luma predictionunits and prediction modes corresponding to chroma prediction units.

According to the present invention, when the prediction mode typeinformation indicates that a linear method (LM) prediction mode is to beimplemented to intra predict a current chroma prediction unit forreconstruction, the LM prediction mode includes obtaining a linearcombination of previously reconstructed luma samples that have beeninterpolated from within a same block of the current chroma predictionunit. The LM mode further includes obtaining a linear interpolation ofpreviously reconstructed luma samples from blocks neighboring thecurrent chroma prediction unit, and obtaining previously reconstructedchroma samples from blocks neighboring the current chroma predictionunit.

Also according to the present invention, when the prediction mode typeinformation indicates that a linear method prediction mode is to be madefor inter predicting a current chroma prediction unit, a method isprovided for obtaining a linear combination of previously reconstructedluma samples that have been interpolated, where the luma samples areobtained from reference pictures that are different from a currentpicture including the current chroma prediction unit. For the interprediction method of the LM prediction mode, utilized reconstructedchroma samples may be obtained from luma samples that have beenreconstructed from reference pictures that are different from thecurrent picture or luma samples that are previously reconstructed on thecurrent picture. Also, reconstructed chroma samples may be directedobtained from a reference picture of the inter prediction mode of the LMprediction mode for inter prediction. The inter prediction method forthe linear method prediction mode is also applicable for B-picturereferences that are reconstructed at a future time.

The LM prediction mode of the present invention also applies to caseswhere a prediction unit may be partitioned into both intra predictionpartition blocks and inter prediction partition blocks.

According to the present invention, the LM prediction mode identifying aprediction process for a chroma sample may be signaled in a manner thatrelies on a previously signaled prediction mode relating to a lumasample. This is done in order to conserve the amount of binary codewordbits needed to identify a proper prediction mode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. First of all, terminologies or words used in thisspecification and claims are not construed as limited to the general ordictionary meanings and should be construed as the meanings and conceptsmatching the technical idea of the present invention based on theprinciple that an inventor is able to appropriately define the conceptsof the terminologies to describe the inventor's invention in an intendedway. The embodiments disclosed in this disclosure and configurationsshown in the accompanying drawings are exemplary in nature and are notintended to be inclusive in nature. The preferred embodiments do notrepresent all possible technical variations of the present invention.Therefore, it is understood that the present invention covers themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents at the timingpoint of filing this application.

For instance a picture may be referred to as a frame, where a frame orpicture represents a single instance of video data. A sequence ofpictures, or frames, comprise the video data. A picture is generallycomprised of a plurality of slices, but it is possible for a singleslice to comprise an entire picture. Also a block can also be referredto as a unit.

Each slice is generally partitioned into a plurality of treeblocks. Thesize of a treeblock is variable, and may have a size as large as 64×64pixels. Alternatively, a treeblock may have a size corresponding to anyone of 32×32, 16×16, 16×8, 8×16, 8×8, 8×4, 4×8, 4×4, 4×2, 2×4 and 2×2pixels. The size of a treeblock is influenced by a variety of factorssuch as, but not limited to, a chosen video resolution of a videopicture. An encoder may also adaptively determine an optimal size for atreeblock throughout the sequence of pictures that comprise the videodata. Another basic unit for processing a video picture is a macroblock.A macroblock has a size of 16×16.

Prior to decoding a transmission of video data, the video data mustfirst be encoded. FIG. 1 illustrates that video data originates from avideo source that provides original video data. Although FIG. 1 depictsthe video source to be part of an overall transmission unit 1, the videosource 2 may be detached from the transmission unit 1 as long as thevideo source 2 is able to communicate the original video data to thetransmission unit 1. In the case where the video source is not anintegral part of the transmission unit 1, it is possible for the videosource 2 to be in direct physical communication with the transmissionunit 1, or in wireless communication with the transmission unit 1.

Prediction processing is performed by a prediction processing unit 3 ofthe transmission unit 1. Prediction processing of the original videodata is necessary to attain a sequence of video data pictures thatrepresents the original video data from the video source. It is whilethe video data is undergoing various prediction processing in theprediction processing unit 3 that prediction mode information isassociated to each prediction unit of video data. The prediction modeinformation identifies under which available prediction mode eachprediction unit was prediction processed. This way, later upon receptionof the video data at a decoding unit, each prediction unit can besuccessfully re-predicted and reconstructed for display by undergoingthe same prediction mode processing as identified by the prediction modeinformation. After going through the prediction processing, a transformunit 4 performs a transform operation on the predicted video data. It ismost likely a Discrete Cosine Transform (DCT) is performed on thepredicted video data. Then the video data is encoded by the encoder unit5 and transmitted.

FIG. 2 depicts a representation of a video data picture according to thepresent invention. The picture in FIG. 2 corresponds to a 4:2:0 samplingrate of the video data. The 4:2:0 sampling rate ensures that for every2×2 luma sample treeblock including 4 luma samples (Y or L), there is apair of corresponding chroma samples (Cr,Cb). In addition to the 4:2:0sampling rate illustrated by FIG. 2, there are various other samplingrates available to transmit the video data. Such other sampling ratesinclude, but are not limited to, a 4:2:2 sampling rate and a 4:4:4sampling rate. While the disclosure for the present invention will bemade under the assumption of a 4:2:0 sampling rate, it is understoodthat all aspects of the present invention are applicable under allavailable sampling rates.

FIG. 3 illustrates a receiver 31 receiving the video data that wastransmitted from the transmitting unit in FIG. 1. The receiver receivesthe video data in a receiving unit 32 along with the correspondingprediction mode information. The decoding unit 33 then decodes the videodata. It is during the decoding of the video data that the correspondingprediction mode information is read to identify the proper predictionmode process to perform for each prediction unit received as part of thevideo data. The inverse transform unit 34 then performs an inversetransform operation on the video data. Most likely it will be an inverseDiscrete Cosine Transform. And the reconstruction unit 35 performs areconstruction of the prediction units that have been processedaccording to the corresponding prediction mode to re-create the videodata for display.

Chroma Intra-Prediction Modes

First, intra prediction modes for predicting chroma samples will beexplained.

A receiver's decoding unit that receives actual video data will alsoreceive intra chroma prediction mode information that corresponds toeach chroma prediction unit of the video data. The chroma sample thatrequires prediction processing at a decoding unit can be referred to asthe chroma prediction unit. The intra chroma prediction mode informationindicates the prediction mode used by an encoder to encode video dataprior to transmission of the video data. This is required so that at thereceiving decoding unit side, the corresponding prediction mode may beprocessed on a prediction unit of video data in order to ensuresuccessful reproduction of the video data. Thus upon receiving thetransmission of video data, the decoding unit is then tasked withreading the intra chroma prediction mode information and then performingthe appropriate prediction on the prediction unit according to the valueindicated by the intra chroma prediction mode information.

TABLE 1 intra_chroma_pred_mode Name of intra_chroma pred_mode 0intra_Chroma_Estimation(prediction mode) 1 intra_Chroma_DC(predictionmode) 2 intra_Chroma_Horizontal(prediction mode) 3intra_Chroma_Vertical(prediction mode) 4 intra_Chroma_Plane(predictionmode)

Table 1 depicts one embodiment of the values and names for the variousintra chroma prediction modes according to one embodiment of the presentinvention. By applying one of these intra chroma prediction modes, acurrent chroma prediction unit can be accurately predicted andreconstructed by a decoding unit.

Table 1 specifically lists a series of values that correspond to aspecific intra chroma prediction mode. Therefore, the intra chromaprediction mode information will include at least a value thatindentifies the corresponding intra chroma prediction mode. When intrachroma prediction mode information has a value of ‘1’, a DC mode forprediction will be applied to a current chroma prediction unit. For a DCprediction mode, previously reconstructed blocks to the left and top ofa current prediction unit, commonly referred to as neighboring blocks,will be utilized to process the prediction of the current predictionunit. FIG. 4(c) depicts an illustrative example for a DC predictionmode. C represents a current prediction unit, A represents previouslyreconstructed blocks to the left of the current prediction unit C, and Brepresents previously predicted block to the top of the currentprediction unit C. According to the DC prediction mode, the mean ofpreviously reconstructed blocks A and B are taken to process theprediction for the current prediction unit C when they are bothavailable. However if only blocks A are available, then the predictionprocessing may follow the horizontal mode explained below. Or if onlyblocks B are available, then the prediction processing may follow thevertical prediction mode explained below. A block is considered to beunavailable when it has not yet been reconstructed or when it is notfrom within a same slice as the current prediction unit.

When intra chroma prediction mode information has a value of ‘2’, ahorizontal mode for prediction will be applied to a current chromaprediction unit. For a horizontal prediction mode, a previouslyreconstructed neighboring block to the left of the current predictionunit will be utilized to process the prediction of the currentprediction unit. FIG. 4(b) depicts an illustrative example for ahorizontal mode prediction. According to the horizontal mode prediction,previously reconstructed blocks A will be used to process a predictionof current prediction unit C.

When intra chroma prediction mode information has a value of ‘3’, avertical prediction mode will be applied to a current chroma predictionunit. For a vertical prediction mode, previously reconstructedneighboring blocks to the top of the current prediction unit will beutilized to process the prediction of the current prediction unit. FIG.4(a) depicts an illustrative example for a vertical mode prediction.According to the vertical mode prediction, previously reconstructedblocks B will be used to process a prediction of current prediction unitC.

When intra chroma prediction mode information has a value of ‘4’, aplane mode for prediction will be applied to a current chroma predictionunit. FIG. 4(d) depicts an illustrative example for a plane modeprediction. Both previously reconstructed blocks to the left and to thetop, A and B respectively, of the current prediction unit C will beutilized to process a prediction of the current prediction unit Caccording to the plane mode.

The explanation for the Estimation prediction mode corresponding to whenthe intra chroma prediction mode information has a value of ‘0’ will beexplained in detail later in the disclosure. For future reference, theEstimation mode is considered to be the same as the LM mode predictionmode described in Table 2 below.

TABLE 2 intra_chroma_pred_mode Name of intra_chroma_pred_mode 0intra_Chroma_LM(prediction mode) 1 intra_Chroma_Vertical(predictionmode) 2 intra_Chroma_Horizontal(prediction mode) 3intra_Chroma_DC(prediction mode) 4 intra_Chroma_DM(prediction mode)

Table 2 depicts a second embodiment for identifying intra predictionmodes to be applied to chroma prediction units according to the presentinvention. Table 2 is considered the preferred embodiment for intrachroma prediction modes for the present invention.

When intra chroma prediction mode information has a value of ‘1’, avertical prediction mode will be applied to a current chroma predictionunit. The vertical prediction mode described in Table 2 operates in thesame manner as the vertical prediction mode described in Table 1 above.

When intra chroma prediction mode information has a value of ‘2’, ahorizontal prediction mode will be applied to a current chromaprediction unit. The horizontal prediction mode described in Table 2operates in the same manner as the horizontal prediction mode describedin Table 1 above.

When intra chroma prediction mode information has a value of ‘3’, a DCprediction mode will be applied to a current chroma prediction unit. TheDC prediction mode described in Table 2 operates in the same manner asthe DC prediction mode described in Table 1 above.

In addition, although not specifically identified in Table 2, an intraangular prediction mode is available for processing a prediction of acurrent chroma prediction unit. The description for the intra angularprediction mode is described below in reference to intra luma predictionmodes. The intra angular prediction mode available for processing chromaprediction units operates in the same manner as the intra lumaprediction mode. Including all of the angular prediction modes, thereare thirty four (34) available intra chroma prediction modes accordingto the preferred embodiment of the invention.

When intra chroma prediction mode information has a value of ‘4’, anintra DM prediction mode will be applied to a current chroma predictionunit. The DM prediction mode is not available in Table 1. The DMprediction mode processes a prediction on a current chroma predictionunit according to a prediction mode applied to a luma sample found inthe same prediction unit as the current chroma prediction unit.

So the intra luma prediction mode information is transmitted andreceived by a decoding mode prior to the intra chroma prediction modeinformation. Thus according to the DM prediction mode, the valuecorresponding to the intra chroma DM prediction mode will simplyindicate a decoding unit to prediction process the current chromaprediction unit in the same mode identified by the intra luma predictionmode information corresponding to luma samples of the same predictionunit. Available intra prediction modes for a luma prediction unit can befound in FIG. 11(a) described later in the disclosure.

When intra chroma prediction mode information has a value of ‘0’, an LM(Linear Method) prediction mode will be applied to a current chromaprediction unit. As mentioned above, the LM prediction mode andEstimation prediction mode are to be understood to operate in the samemanner, and may be referenced according to either name throughout thedisclosure.

Intra LM Prediction Mode

A detailed description for the intra LM chroma prediction mode will nowbe given. When receiving a video data transmission, a decoder will firstpredict and reconstruct (ie. decode), luma prediction units of a givenblock prior to predicting and reconstructing chroma prediction units ofthe same block. FIG. 5 illustrates a slice according to the presentinvention that is partitioned into 4 blocks. Assuming that blocks B1, B2and B3 have already been prediction processed and reconstructed by adecoding unit of a receiver, it is taken that B4 is currently beingprediction processed for reconstruction. And within block B4, the upperlefthand corner of block B4 will be taken for exemplary purposes toembody a current block C currently being prediction processed.

FIG. 6 is then a magnified view of the box area outlined in dashed linesin FIG. 5. FIG. 6 illustrates a 32×32 size depiction of block C that iscurrently being prediction processed. Each of the white blocks outlinedin block C represents a luma sample that has already been predictionprocessed and reconstructed. Therefore only the chroma samples of theblock C need to be prediction processed. Adjacent to block C areneighboring blocks A and block B. Block A is a partial representation ofB1 located to the left of block C, as seen in FIG. 5. And block B is apartial representation of B2 located to the top of block C, as seen inFIG. 5. Both block A and block B have already been reconstructed.

FIG. 7 illustrates a further close up view of a 4×4 size block from theupper lefthand portion of the current prediction block C seen in FIG. 6.FIG. 7 also provides a 2×4 size partial block view of the adjacent blockA to the left of block C. And FIG. 7 also provides a 4×2 size blockpartial block view of the adjacent block B to the top of block C.Because blocks A and B have already been reconstructed, the white blocksof blocks A and B represent luma samples that have already beenreconstructed, and the black squares represent sets of chroma samplesthat have already been reconstructed. It is noted that although notvisible due to the black reconstructed chroma blocks, there is also acorresponding reconstructed luma sample behind each black chroma samplein blocks A and B. Therefore, the luma samples of the current block Chave already been reconstructed, the luma samples of the neighboringblocks A and B have already been reconstructed, and the chroma samplesof the neighboring blocks A and B have already been reconstructed. Andthe ‘X’ marks in blocks A and B represent a linear interpolation ofreconstructed luma samples from each corresponding blocks A and B. Thesereconstructed luma and chroma samples from neighboring blocks, andlinear interpolation of luma samples from neighboring blocks, will allplay a role in the LM prediction mode processing for chroma predictionunits of the current block C.

In order to perform an intra chroma prediction for a current chromaprediction unit in block C according to an LM mode, a linearinterpolation of previously reconstructed luma samples within thecurrent prediction block C must first be attained.

According to a preferred embodiment of the intra LM prediction mode, twopreviously reconstructed luma samples are obtained from within block C.A previously reconstructed luma sample is denoted by P_(L)(x,y), where xand y correspond to location references for a current chroma predictionunit within block C that is currently being prediction processedaccording to the LM prediction mode. A first luma sample is taken atP_(L)(2x,2y) and a second luma sample is taken at P_(L)(2x,2y+1) withinblock C. Then according to the preferred embodiment of the intra LMprediction mode, the linear combination of interpolated luma samples,P_(L*)(x,y), can be attained byP _(L*)(x,y)=0.5*[P _(L)(2x,2y)+P _(L)(2x,2y+1)]  [Math Figure 1]

Now with the attained linear combination of interpolated luma samples,P_(L*)(x,y), the intra LM prediction for the current chroma predictionunit, denoted by P′_(c), can be attained byP′ _(c)=α*0.5*P _(L*)+β  [Math Figure 2]where alpha, α, and beta, β, can be attained by

$\begin{matrix}{{\alpha = \frac{R( {{\hat{P}}_{L^{*}},{\hat{P}}_{C}} )}{R( {{\hat{P}}_{L^{*}},{\hat{P}}_{L^{*}}} )}}{\beta = {{M( {\hat{P}}_{C} )} - {\alpha \times {M( {\hat{P}}_{L^{*}} )}}}}} & \lbrack {{Math}\mspace{14mu}{Figure}\mspace{14mu} 3} \rbrack\end{matrix}$

According to Math Figure 3, R(*,*) represents a correlation between thetwo references variables, and M(*) represents an average for thevariable referenced within. P^_(L*) represents a linear interpolation ofa previously reconstructed luma sample taken from either one ofneighboring blocks A or B. According to FIG. 7, P^_(L*) is representedby the ‘X’ marks found in either of neighboring blocks A or B. AndP^_(C) represents a reconstructed chroma sample taken from either one ofneighboring blocks A or B. According to FIG. 7, P^_(C) is represented bythe black blocks in either one of neighboring blocks A or B. P^_(L*) mayalso implement a left or right shift function to account for anyrounding errors that may occur.

FIG. 8 is the same close up view of the upper lefthand portion of blockC as seen in FIG. 7. However FIG. 8 additionally depicts the resultinglinear combination of interpolated luma samples within block C as markedby the ‘X’ marks within block C. Luma samples 1 and 3 represent thepreviously reconstructed luma samples attained by P_(L)(2x,2y) when(x,y)=(0,0) and (x,y)=(1,0) respectively. And luma samples 2 and 4represent the reconstructed luma samples attained by P_(L)(2x,2y+1) when(x,y)=(0,0) and (x,y)=(1,0) respectively. The black block units found inblock A neighboring to the left of current block C and the black blockunits found in block B neighboring to the top of current block C, arerepresentations of previously reconstructed chroma samples that can beused to attain the α and β coefficients in Math Figure 3. The ‘X’ marksfound in block A neighboring to the left of current block C and the ‘X’marks found in block B neighboring to the top of current block C, arerepresentations of linear interpolations of previously reconstructedluma samples that can be used to attain the α and β coefficients in MathFigure 3.

As mentioned above, FIG. 8 shows the result of attaining the linearcombination of interpolated luma samples according to P_(L)*(x,y). Byway of example, taking luma sample 1 and luma sample 2, and applying thelinear combination of interpolated luma samples according P_(L*)(0,0),the result is indicated by the ‘X’ mark found in between luma sample 1and luma sample 2 in FIG. 8.

Similarly, the ‘X’ found in between luma sample 3 and 4 represents theresulting linear combination of interpolated luma samples according toP_(L*)(1,0). The remaining ‘X’ marks seen in FIG. 8 represent the linearinterpolation resulting from P_(L*)(0,1) and P_(L*)(1,1) based on theremaining previously reconstructed luma samples found in the currentblock C. The α and β coefficients can be attained from the adjacentblocks A and B.

Now in order to process the actual intra chroma prediction, the linearcombination of interpolated luma samples attained above, P_(L*)(x,y),are collaborated along with the calculated α and β coefficients to thenattain the intra chroma LM prediction, P′_(c)(x,y), for the currentchroma prediction unit. The exact calculation for the current chromaprediction unit according to the intra chroma LM prediction mode can beseen in Math Figure 3.

However, the present invention is not limited to only include a linearcombination of interpolated luma samples as depicted in FIG. 8. In asecond alternative embodiment for attaining a linear combination ofinterpolated luma samples, P_(L)*(x,y), two different luma samples maybe taken. FIG. 9 represents the second embodiment, and depicts the sameclose up view of the upper lefthand corner of current block C asdepicted in FIG. 8. However, in FIG. 9 the resulting linear combinationof interpolated luma samples have shifted one unit to the right comparedto the result of the linear combination of interpolated luma samples asseen in FIG. 8. This shift can be accomplished by incorporating a shiftin the luma samples taken when attaining P_(L*)(x,y). Thus according tothe second embodiment, a first luma sample may be taken atP_(L)(2x−1,2y), and the second luma sample may be taken atP_(L)(2x+1,2y+1).

So by shifting the luma samples from which to take the linearinterpolation with, the second embodiment is able to provide furtherflexibility to the LM prediction mode. FIG. 9 depicts the resultinglinear combination of interpolated luma samples according to the secondembodiment by the location of the ‘X’ marks within block C.

The P_(L*)(x,y) according to the second embodiment is attained byP _(L*)(x,y)=0.5*[P _(L)(2x+1,2y)+P _(L)(2x+1,2y+1)]  [Math Figure 4]

The calculations for the coefficients α and β remain the same as seen inMath Figure 3 by attaining the linear interpolation of previouslyreconstructed luma samples, and previously reconstructed chroma samplesfrom the neighboring blocks A and B. And similarly, the actual intra LMprediction for a current chroma prediction unit, P′_(c), is stilldefined by Math Figure 2. The only difference according to the secondembodiment is the result of the linear combination of interpolated lumasamples, P_(L*)(x,y), that is due to a shift in luma samples takenwithin the current block C.

In a third embodiment for attaining a linear combination of interpolatedluma samples, P_(L*)(x,y), four different luma samples may be taken fromwithin the current block C. FIG. 10 represents the third embodiment.FIG. 10 is the same close up portional view of the upper lefthand cornerof the current block C as depicted in FIGS. 8 and 9. However, accordingto the third embodiment, four previously reconstructed luma samples aretaken from block C to attain the P_(L*)(x,y) instead of just the 2 asdescribed in the first and second embodiments. These four previouslyreconstructed luma samples are marked as 1, 2, 3 and 4 in FIG. 10. Thefirst luma sample, 1, can be attained by P_(L)(2x,2y). The second lumasample, 2, can be attained by P_(L)(2x+1,2y). The third luma sample, 3,can be attained by P_(L)(2x,2y+1). And the fourth luma sample can beattained by P_(L)(2x+1,2y+1). By taking the average of the four attainedluma samples, the linear interpolation, P_(L*)(x,y), according to thethird embodiment can be attained. The ‘X’ mark found in the middle ofluma samples 1, 2, 3 and 4 is a linear interpolation of the fourpreviously reconstructed luma samples according to the third embodiment.The remaining ‘X’ marks depict the results from linear interpolationsattained from the remaining previously reconstructed luma samples ofcurrent block C.

Thus the P_(L*)(x,y) according to the third embodiment can be attainedbyP _(L*)(x,y)=0.25*[P _(L)(2x,2y)+P _(L)(2x+1,2y)+P _(L)(2x,2y+1)+P_(L)(2x+1,2y+1)]  [Math Figure 5]

The calculations for the coefficients α and β remain the same as seen inMath Figure 3 by attaining the previously reconstructed luma and chromasamples from the adjacent blocks A and B. Therefore, according to thethird embodiment, the intra chroma LM prediction for a current chromaprediction unit, P′_(c), is still defined by Math Figure 2. The onlydifference occurs from the different result from the linearinterpolation, P_(L*)(x,y), due to the increase in luma samples beingtaken.

It is to be understood that the methods for attaining P_(L)*(x,y) arenot limited to the embodiments disclosed above. The above disclosedembodiments for attaining P_(L)*(x,y) have been made to demonstratepreferable embodiments thereof, however it will be understood by thoseskilled in the art that various methods for attaining a linearinterpolation of reconstructed luma samples are possible under thepresent invention without departing from the scope and spirit of thepresent invention.

Chroma Inter Prediction Modes

Chroma samples of inter prediction blocks did not previously have theirown prediction modes. It was the case that chroma samples of an interprediction block were prediction processed simply by following aprediction mode for a corresponding luma sample in a same predictionunit. However, according to the present invention, the LM predictionmode described in terms of intra chroma prediction is made available forinter chroma prediction.

Inter predictions also involve prediction processing the luma samplesprior to processing the chroma samples of any given prediction unit.This means that previously reconstructed luma samples are available whenprocessing a prediction on a current chroma prediction unit. Thereforethe basic processing for inter chroma LM prediction will be processedthe same as described above for intra chroma LM prediction. The onlydifference is that for inter prediction, luma samples belonging to thesame prediction unit as the current chroma prediction unit, arereconstructed by making reference to reference pictures that aredifferent from a current picture that includes the current chromaprediction unit.

Therefore, although the method for reconstructing luma samples aredifferent according to the intra prediction mode and inter predictionmode, after obtaining reconstructed luma samples belonging to a sameprediction unit, a chroma prediction unit can be prediction processed inan inter LM prediction mode. Then the reconstructed luma samplesincluded in the same prediction unit can be taken to form a linearcombination and then interpolated for processing of an inter chroma LMprediction mode. Similarly the α and β coefficients seen in Math Figure3 may be attained by utilizing motion vector compensation to process thereconstruction of luma and chroma samples in prediction unitsneighboring the current chroma prediction unit. And a linearinterpolation may be applied to a neighboring luma sample to obtain theα and β coefficients.

And once the linear combination of previously reconstructed luma samplesare interpolated, and the necessary luma and chroma samples needed tocalculate the α and β coefficients seen in Math Figure 3 are obtained,the inter chroma LM prediction mode can be processed on the currentchroma prediction unit according to Math Figure 2.

Signaling for Intra Chroma LM Prediction Mode

Transmission of a video signal will include encoded video data arrangedinto block data formats, wherein the blocks contain luma samples andchroma samples that are a prediction from an original video source. Alsoincluded in the video signal along with the actual video data will be avariety of information data relating to various characteristics of thevideo data. The information data may include size information forblocks, instructional flags and block type information among otherpossible information data. Among the variety of information dataincluded in the transmission signal, there will be prediction modeinformation relating to each block of encoded video data. The predictionmode information indicates which available prediction mode was used toencode video data. The prediction mode information is transmitted alongwith the encoded video data so that a decoder that receives the encodedvideo data can which prediction mode was used for prediction processingat the encoding unit, so that the same prediction mode can be used toaccurately reconstruct the video data at the decoding unit.

In any prediction process for reconstruction of a block in a decoder,the luma samples are the first to be prediction processed. So forexample in a 2×2 pixel size block found in 4:2:0 sampling, there will befour luma samples and a set of corresponding chroma samples. And in thiscase, the four luma samples will be prediction processed forreconstruction before the corresponding set of chroma samples.

In a preferred embodiment, there are thirty four (34) intra predictionmodes available, when including each of the angular modes (3 . . . 33).FIG. 11(a) depicts the thirty four intra prediction modes according tothe preferred embodiment. As can be seen from FIG. 11(a), the verticalprediction mode, horizontal prediction mode and DC prediction mode areavailable for intra luma prediction. The angular prediction mode alsoseen in FIG. 11(a) is available for both intra luma prediction and intrachroma prediction. The intra chroma angular prediction mode may beprocessed on a current chroma prediction unit by identifying the DMprediction mode as the intra chroma prediction mode when thecorresponding intra luma prediction mode is the angular prediction mode.The processing for the vertical prediction mode, horizontal predictionmode and DC prediction mode prediction modes are described above withreference to FIGS. 4(a)-(c). The DM prediction mode is unique to intrachroma prediction.

A more detailed description for the angular prediction mode will now begiven. The intra Angular prediction mode, corresponding to intraprediction mode information values ‘3-33’, predicts a current predictionunit based on an angular representation of previously predicted samplesthat adjacently neighbors the current prediction unit at an anglecorresponding to the angles depicted in FIG. 12. As seen in FIG. 12,each value between ‘3-33’ for the intra luma prediction modes actuallycorresponds to a distinct angular prediction mode. FIG. 12 also depictsan illustrative depiction for the intra DC prediction mode having acorresponding intra prediction mode information value of ‘2’.

While the preferred embodiment for intra luma prediction modes depictedin FIG. 11(a) does not include a separate intra luma LM prediction mode,an alternative embodiment may include such an LM prediction mode forprocessing intra predictions of luma samples. FIG. 11(b) depicts thealternative embodiment that includes the intra luma LM prediction mode.For ease of explanation the LM intra prediction mode was given the valueof ‘34’ in the table depicted by FIG. 11(b). This allows the thirty fourintra luma prediction modes from the preferred embodiment depicted inFIG. 11(a) to keep their original values in the alternative embodimentdepicted in FIG. 11(b). However the value assigned to the intra luma LMprediction mode is not limited to the ‘34’ depicted in FIG. 11(b).

For instance, another alternative embodiment may assign the intra lumaLM prediction mode a value of ‘3’. In this alternative embodiment thevertical prediction mode is assigned a value of ‘0’, the horizontalprediction mode is assigned a value of ‘1’, the DC prediction mode isassigned a value of ‘2’, the LM mode is assigned a value of ‘3’ and theangular prediction mode is assigned the remaining values ‘4 . . . 33’. Atable for identifying this third alternative embodiment is detailed byTable 3 below.

TABLE 3 intraPredMode Name of intraPredMode 0 Intra_Vertical 1Intra_Horizontal 2 Intra_DC 3 Intra_LM Otherwise (4 . . . 34)Intra_Angular

While only the three embodiments for possible intra prediction modes forluma samples have been explained herein, it is within the scope of thepresent invention to switch the prediction mode values for any of theprediction modes shown to be available according to the intra lumaprediction modes disclosed above. As long as each of the availableprediction modes can be clearly distinguish and not confused withanother prediction mode, any value may be assigned to each of theavailable prediction modes for intra luma prediction processing. Thisholds true for the numbering of the intra chroma prediction mode valuesas well.

FIG. 13 depicts a representation of a prediction circuit for determiningthe proper intra prediction mode within a video signal receiving unit.The IntraPredMode illustrates intra prediction mode information assignedfrom an encoding unit prior to transmission for identifying a properintra prediction mode for processing a luma prediction unit. Theintra_chroma_pred_mode illustrates intra prediction mode informationassigned by an encoding unit prior to transmission for identifying aproper intra prediction mode for processing a chroma prediction unit.And the Prediction Unit illustrates the video data that is received bythe receiving decoding unit to be prediction processed according to acorresponding intra prediction mode. Although FIG. 13 depicts thePrediction Unit being input to the Selector 131 along with the intraprediction mode information, it is within the scope of the presentinvention that the Prediction Unit data bypasses the Selector and isdirectly inputted into the prediction unit 132.

For an intra luma prediction process, a luma Prediction Unit along witha corresponding IntraPredMode information is input to the selector 131.The available IntraPredMode are disclosed in FIGS. 11(a) and 11(b), asexplained above. Because intra luma prediction mode information isreceived prior to intra chroma prediction mode information, the lumaPrediction Unit will be directly according to the correspondingIntraPredMode information. Thus the selector 131 need only outputIntraPredMode to the prediction unit 132 where the IntraPredModeinformation will identify the proper intra prediction mode forprocessing a prediction for the luma prediction unit. The lumaprediction unit is then processed directly in the prediction unit 132according to the intra prediction mode identified by the IntraPredModeinformation. After the luma prediction unit is prediction processedaccording to the intra prediction mode available in the prediction unit132, the reconstructed luma prediction unit is then output for display.In addition, the IntraPredMode information will be fedback to theselector 131 for use when chroma prediction units from the same blockwill be prediction processed later.

FIG. 17 illustrates a possible sequence of determinations that must bemade by the selector 131 when determining a proper output forinstructing the prediction unit to perform the properintra_chroma_pred_mode on an intra chroma prediction unit. Afterreceiving the IntraPredMode information in step S1701 and processing theluma prediction units according to the IntraPredMode in step S1702,chroma prediction units will be input to the selector 131 along withcorresponding intra_chroma_pred_mode information in step S1703. If theintra_chroma_pred_mode information identifies an Intra_DM predictionmode, then the selector 131 must refer to the previously processedIntraPredMode that was fedback to the selector 131 in step S1705. If theintra_chroma_pred_mode does not identify the Intra_DM prediction mode,then the selector reads the intra_chroma_pred_mode information andoutputs the proper information to the prediction unit 132 to process thecorresponding intra_chroma_pred_mode in steps S1707, S1709, S1711 andS1713. Although FIG. 17 depicts a selector going through the sequence ofdetermining whether the infra_chroma_pred_mode information identifies anIntra_LM prediction mode at S1706, to whether it identifiesIntra_Vertical prediction mode, to whether it identifiesIntra_Horizontal and finally whether it identifies Intra_DC predictionmode, the selector according to the present invention is not limited toalways adhering to such a sequence. Any sequence of determination ofidentifying intra_chroma_pred_mode is within the scope of the presentinvention. Also, although FIG. 17 depicts a sequence of determinationsteps being followed, according to a preferred embodiment of the presentinvention luma and chroma samples of a same prediction unit may beprediction processed in parallel. In other words all luma samples of aprediction need not be actually completely prediction processed beforeprediction processing a corresponding chroma sample of the same sampleunit. As long as the intra luma prediction mode information is received,a decoding unit may begin the process for prediction processing thecorresponding chroma sample according to the DM prediction mode. Thusoperationally, as soon as selector 131 receives IntraPredModeinformation identifying a prediction mode for the luma sample,prediction processing for a chroma sample of the same prediction unitcan be initiated in parallel.

The mapping table depicted in FIGS. 14(a) and 14(b) maps the intra lumaprediction mode information, IntraPredMode, and intra chroma predictionmode information, intra_chroma_pred_mode, that is transmitted along withencoded video data. The result of such intra prediction mode informationbeing assigned for transmission is represented in the cross matchingbody of the mapping tables. The resulting value from the mapping tablesof FIG. 14(a) and FIG. 14(b) may be referred to as IntraPredModeC. Themapping tables are to be understood from the standpoint of each instanceof a received IntraPredMode value.

For example, if the previously received IntraPredMode is ‘0’,corresponding to an Intra_Vertical prediction mode, then the values thatwill be assigned to each of the available intra chroma prediction modesin this instance will be found below within the same column. So stayingunder the assumption that IntraPredMode identifies the Intra_Verticalprediction mode, if the selector 131 receives a value of ‘0’ forintra_chroma_pred_mode, then according to FIG. 14(a) IntraPredModeC willcorrespond to a value of ‘34’. Then referring back to FIG. 11(b) it isseen that ‘34’ identifies the Intra_LM prediction mode.

Staying under the assumption that IntraPredMode still identifies theIntra_Vertical prediction mode, if the Intra_Vertical prediction mode isto be signaled for chroma prediction there is no need for theintra_chroma_prediction_mode information to specifically transmit thevalue for Intra_Vertical prediction mode, thus the ‘n/a’ value. This isbecause information pertaining to the Intra_Vertical prediction mode isalready known from the intra luma prediction, and Intra_Verticalprediction mode can be invoked by simply referring to the Intra_DMprediction mode. The Intra_DM prediction mode allows the chromaprediction mode to follow the corresponding luma prediction mode. Sowhen IntraPredMode is the Intra_Vertical prediction mode, there is noneed to specifically assign a value for Intra_Vertical prediction modefor the chroma sample due to the availability of the Intra_DM predictionmode. For all other prediction modes while IntraPredMode has a value‘0’, a specific value must be assigned to specify the proper intrachroma prediction mode. So when IntraPredMode is still ‘0’ and theselector 131 subsequently receives an intra_chroma_pred_mode of ‘3’,then the selector 131 will know that an Intra_DC prediction mode isbeing signaled. Then referring back to FIG. 11(b), it is seen thatIntra_DC prediction mode corresponds to the value ‘2’. And this is whatis depicted as the IntraPredModeC result of FIG. 14(a).

Now when IntraPredMode is the Intra_Horizontal prediction mode ‘1’,there is similarly no need for the intra_chroma_pred_mode information tospecifically transmit the value relating to the Intra_Horizontalprediction mode, thus the ‘n/a’ value seen in Table 14(a). Instead whenIntraPredMode has a value ‘1’ and intra_chroma_pred_mode has a value‘4’, then the resulting IntraPredModeC from Table 14(a) is ‘1’, whichidentifies the Intra_Horizontal prediction mode as seen in FIG. 11(b).However if IntraPredMode has a value of ‘1’ and an Intra_DC predictionmode is desired for intra chroma prediction, IntraPredModeC, thenintra_chroma_pred_mode has a value of ‘3’, and this corresponds to avalue of ‘2’ in the mapping table of FIG. 14(a). Where in FIG. 11(b),‘3’ is seen to identify the Intra_DC prediction mode.

Chroma prediction units may be prediction processed according to theIntra_Angular prediction mode when IntraPredMode indicates intra lumaangular prediction mode, and intra_chroma_pred_mode identifies theIntra_DM prediction mode.

By utilizing the Intra_DM prediction mode, bits of a binary codewordcorresponding to each intra prediction mode can effectively be conservedand reduced. This savings in bits becomes more apparent when viewingFIG. 14(b) and FIG. 15. FIG. 14(b) is the same mapping table as depictedin FIG. 14(a) except the numerical values have been swapped out for thebinary bitstream codeword bits that are actually transmitted in adigital signal. For cases where the IntraPredMode value that istransmitted first corresponds to the Intra_Vertical, Intra_Horizontaland Intra_DC prediction modes (0, 1, 2), the binary bit codewordrequired to signal the appropriate intra chroma prediction mode can beshortened to a maximum of three bits. This is because the Intra_DMprediction mode allows for one of the commonly shared prediction modesto become obsolete in these cases, as represented by the ‘n/a’. Thesignificance of the Intra_DM prediction mode, then, is that for eachinstance where IntraPredMode identifies one of the Intra_Vertical,Intra_Horizontal and Intra_DC prediction modes (0, 1, 2), the ‘n/a’ inthe mapping table of FIG. 14(b) indicates that the encoding unit is freefrom assigning a separate codeword value for the corresponding intrachroma prediction mode. So one less intra prediction mode needs to beassigned a codeword thanks to the Intra_DM prediction mode.

From a binary bit codeword standpoint, this allows for the use of maxthree bit codewords of ‘0’, ‘10’, ‘111’ and ‘110’ to assign to the fourintra chroma prediction modes that need to be separately distinguishedwhen the IntraPredMode corresponds to Intra_Vertical, Intra_Horizontaland Intra_DC prediction modes. If the Intra_DM prediction mode were notavailable, then in all instances five separate intra chroma predictionmodes would need to be distinguished. If five distinct codewords areneeded, then this increases the necessary codeword bit length toincrease to a maximum of four bits. This can be seen in the case wherethe IntraPredMode is the Intra_Angular prediction mode. In this case,each intra prediction modes must be assigned one of ‘0’, ‘10’, ‘110’,‘1111’, ‘1110’ binary codewords. During a binary bitstream it isdifficult to distinguish between ‘1’, ‘11, ‘111’ and ‘1111’ and thusmore than one of these codeword values are preferred not to be used whenassigning to an intra chroma prediction mode for each IntraPredModeinstance.

It is noted that each instance of the IntraPredMode may assign its ownbinary bit codeword to correspond to an intra chroma prediction mode.This is why for the case where IntraPredMode is ‘0’, the codeword valueto signal Intra_DC prediction mode for chroma samples can be ‘110, andfor the case where IntraPredMode is ‘2’, the codeword value to signalIntra Horizontal prediction mode for a chroma sample can also beassigned ‘110’. Each instance of IntraPredMode can assign its owncodeword value for the available intra chroma prediction modes.According to a preferred embodiment of the present invention, theIntra_DM prediction mode will be assigned the binary codeword ‘0’corresponding to the shortest binary bit length. Also according to apreferred embodiment of the present invention, the Intra_LM predictionmode will be assigned the binary codeword having the second shortestbinary bit length, ‘10’.

However, it is within the scope of the present invention to assign anyone of the codewords to any one of the available prediction modes shownin FIG. 15 in alternative embodiments.

For example, if it is later determined that intra chroma samples areincreasingly being predicted according to the Intra_DC mode, then theIntra_DC prediction mode may be assigned the codeword ‘0’ to conservethe amount of codeword bits that need to be transmitted. It is alsowithin the scope of the present invention to adaptively change theassignment of prediction mode codewords during the transmission orreception of a video signal. For instance if it is determined thatcertain video sequences require a large number of Intra_LM modeprediction processing, then for those video sequences the Intra_LMprediction mode may be assigned the codeword with the smallest number ofbits, ‘0’. Then later if another video sequence within the video signalfinds that a large number of Intra_Horizontal prediction mode processingis required, then the Intra_Horizontal prediction mode may be assignedthe codeword having the smallest number of bits, ‘0’. Therefore it iswithin the scope of the present invention to adaptively assign binarycodeword values for prediction mode identification in an effort toconserve the total number of bits that need to be transmitted.

In the alternative embodiment where the Intra_LM prediction mode is madeavailable for the prediction processing of luma samples, the mappingtable may be depicted as shown below in Table 4. According to Table 4,the Intra_LM prediction mode corresponds to IntraPredMode having a valueof ‘3’, whereas the values for intra_chroma_pred_mode remain the same asseen in FIG. 14(a). As mentioned regarding FIG. 11(b), the valueassigned to IntraPredMode for identifying the Intra_LM prediction modefor luma samples, may be changed adaptively. Thus the makeup of Table 4may also change depending on the value assigned to IntraPredMode foridentifying the Intra_LM prediction mode for luma samples.

TABLE 4 IntraPredMode[ xB ][ yB ] intra_chroma_pred_mode 0 1 2 3 X (4 <=X <= 34) 0 3 3 3 n/a 3 1 n/a 0 0 0 0 2 1 n/a 1 1 1 3 2 2 n/a 2 2 4 0 1 23 X

The steps for determining which binary codeword value to transmit froman encoder with respect to an intra chroma prediction mode according toa preferred embodiment is outlined in FIG. 16.

FIG. 18 describes an alternative embodiment for identifying when theIntra_LM prediction mode is to be selected as the proper intra chromaprediction mode by a decoding unit. The alternative embodimentillustrated in FIG. 18 operates in much the same way as the preferredembodiment illustrated in FIG. 17. However the alternative embodiment inFIG. 18 contemplates receiving an Intra_LM prediction mode flag as partof the transmitted prediction mode information. If for some reason anIntra_LM prediction mode flag is missing from the received predictionmode information, step S1806 provides that prediction processing ishandled according to the preferred embodiment outlined in FIG. 17. Ifthe Intra_LM prediction mode flag is received, then it is determinedwhether the Intra_LM prediction mode flag has a first value (eg. valueof ‘1’) indicating an Intra_LM prediction mode is to be processed S1804.If the Intra_LM prediction mode flag does have the first value, then acurrent chroma prediction unit will automatically undergo the Intra_LMprediction mode processing S1805. If the Intra_LM prediction mode flaghas a second value indicating an Intra_LM prediction mode is not to beprocessed, then the current intra chroma prediction unit will be handledaccording to the preferred embodiment outlined in FIG. 17 starting fromS1806.

FIG. 19 describes yet another alternative embodiment for signaling theLM prediction mode is to be processed by a decoding unit for a chromaprediction unit. After a most_probable_chroma_mode_flag is receivedS1901, if the most_probable_chroma_mode_flag has a first value (eg.‘1’), then the chroma_prediction_mode will follow the current modeidentified for the most_probable_chroma_mode. Themost_probable_chroma_mode is defined as min(chroma_prediction_mode_A,chroma_prediction_mode_B) if both A and B are available S1904. A and Brefer to blocks neighboring a current block C that includes the currentchroma prediction unit that requires prediction processing. Both block Aand block B are assumed to be previously reconstructed and thusavailable for determining which prediction mode was used to reconstructthem. Thus the min(A,B) function compares the values of the predictionmode used to reconstruct block A and block B, where the actual numericalvalues can be obtained according to the values found in either Table 1or Table 2. As an alternative, a max(A,B) function may be appliedinstead of the min(A,B) function. And in yet another alternative,multiple blocks (A, B, C, etc. . . . ) may be taken to apply the min( )max( ) or any other applicable function.

If neighboring blocks A and B are not available, then thechroma_prediction_mode is automatically identified as the Intra_DCprediction mode S1904. A neighboring block is considered not to beavailable when the neighboring block is not within the same slice as thecurrent block C, or if the neighboring block is not an intra predictedblock. At the end of the processing in S1904, whatever the current valuedetermined for chroma_prediction_mode will be transmitted to identify anintra chroma prediction mode for prediction processing the currentchroma sample.

If the most_probable_chroma_mode_flag has a second value, then thechroma_prediction_mode is compared against the most_probable_chroma_modeS1903. If the chroma_prediction_mode has a value less than themost_probable_chroma_mode, then the current value forchroma_prediction_mode is transmitted for prediction processing S1905.If the chroma_prediction_mode has a value that is not less than themost_probable_chroma_mode, then an intra chroma prediction modecorresponding to an identification value of one less than thechroma_prediction_mode will be transmitted for prediction processing. Oras an alternative, if the chroma_prediction_mode has a value that is notless than the most_probable chroma_mode, then an intra chroma predictionmode corresponding to an identification value of one more than thechroma_prediction_mode will be used for prediction processing. And inyet another alternative, if the chroma_prediction_mode has a value thatis not less than the most_probable_chroma_mode, then any of theavailable intra chroma prediction modes available may be set as adefault mode for prediction processing. For example an Intra_DC mode maybe used in this alternative.

While the description has thus far been made for all cases of intrachroma prediction processing, the present invention also considersmaking the Intra_LM prediction mode only available for certain sizes ofchroma transform units. A chroma transform unit is determined during theencoding process and refers to the size of the chroma sample that willbe transformed (ie. during the DCT transform process). Thus the chromatransform unit size must be determined by an encoding unit prior toassigning a prediction mode type when preparing the information fortransmission. For instance the Intra_LM prediction mode may beunavailable for chroma prediction when the chroma sample transform unitsize is larger than 8 (ie. 8×8 pixels). In this case the size of thechroma transform unit must first determined before assigning theprediction mode type. Likewise, when receiving the video datatransmission, the decoding unit will receive and read the chromatransform unit size information before reading the prediction mode type.This ensures that the decoding unit will realize when an Intra_LMprediction mode will not be made available.

If the availability of the Intra_LM is set to depend on the size of achroma transform unit, it stands that information identifying the sizeof the chroma transform unit must be transmitted prior to thetransmission of the information indicating the prediction mode type.FIGS. 20 and 21 provide an illustration of how on the decoding unitside, the transform unit size will be identified prior to identifying anintra prediction mode type. Because the transmission signal inputs thetransform unit size information, before the prediction mode typeinformation, this ensures that the decoding unit will parse thetransform unit size information before parsing the prediction mode typeinformation.

Although the transform unit size of 8 is specifically mentioned, it iswithin the scope of the invention to choose a different transform sizefor determining when to cut off the availability of the Intra_LMprediction mode for chroma prediction processing. In the event that theIntra_LM prediction mode is not made available, an alternativeprediction mode such as an Intra_Vertical8 prediction mode may beassigned. It is within the scope of the present invention that insteadof the Intra_Vertical8 prediction mode, another available intraprediction mode is assigned.

Also, according to a preferred embodiment the chroma transform unit sizeis set to automatically equal the transform unit size of a correspondingluma transform unit size. Thus according to the preferred embodimentseen in FIGS. 20 and 21 the transform unit size identifying the lumatransform unit size will be taken as the chroma transform unit size.However, it is within the scope of the present invention that thetransform unit size for a chroma may be determined independent from theluma transform unit size. In this alternative, the transmission ofinformation will include chroma transform unit size information. And thechroma transform unit size information will be transmitted such that thechroma transform unit size information will be parsed by the decodingunit prior to parsing a prediction mode type.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

What is claimed is:
 1. A method for decoding, by a decoding apparatus, abitstream for a coded video signal comprising at least one block, themethod comprising: determining, by the decoding apparatus, predictiontype information of a current block, the prediction type informationindicating whether the current block is intra-coded or inter-coded;determining, by the decoding apparatus, a luma intra prediction mode ofthe current block when the prediction type information indicates thatthe current block is intra-coded, the luma intra prediction modespecifying an intra prediction mode for luma samples of the currentblock; obtaining, by the decoding apparatus, index information of thecurrent block from the bitstream, the index information being used tospecify an intra prediction mode for chroma samples of the currentblock; deriving, by the decoding apparatus, a chroma intra predictionmode according to a predefined mapping table based on the determinedluma intra prediction mode and the obtained index information; anddecoding, by the decoding apparatus, the chroma samples of the currentblock based on the derived chroma intra prediction mode, wherein, whenthe obtained index information has a predefined value, the chroma intraprediction mode is set equal to the luma intra prediction mode.
 2. Themethod of claim 1, wherein the predefined mapping table defines arelationship between the derived chroma intra prediction mode and acombination of the determined luma intra prediction mode and theobtained index information.
 3. The method of claim 1, wherein thedetermining of the luma intra prediction mode includes: obtaining flaginformation indicating whether the luma intra prediction mode is derivedbased on intra prediction modes of neighboring blocks of the currentblock, and determining the luma intra prediction mode based on the intraprediction modes of the neighboring blocks when the flag informationindicates that the luma intra prediction mode is derived based on theneighboring blocks of the current block.
 4. The method of claim 1,wherein the predefined value is equal to
 4. 5. An apparatus for decodinga bitstream for a coded video signal comprising at least one block, theapparatus comprising: a receiving unit configured to receive thebitstream; and a decoding unit configured to: determine prediction typeinformation of a current block, the prediction type informationindicating whether the current block is intra-coded or inter-coded,determine a luma intra prediction mode of the current block when theprediction type information indicates that the current block isintra-coded, the luma intra prediction mode specifying an intraprediction mode for luma samples of the current block, obtain indexinformation of the current block from the bitstream, the indexinformation being used to specify an intra prediction mode for chromasamples of the current block, derive a chroma intra prediction modeaccording to a predefined mapping table based on the determined lumaintra prediction mode and the obtained index information, and decode thechroma samples of the current block based on the derived chroma intraprediction mode, wherein, when the obtained index information has apredefined value, the chroma intra prediction mode is set equal to theluma intra prediction mode.
 6. The apparatus of claim 5, wherein thepredefined mapping table defines a relationship between the derivedchroma intra prediction mode and a combination of the determined lumaintra prediction mode and the obtained index information.
 7. Theapparatus of claim 5, wherein the decoding unit is further configured todetermine the luma intra prediction mode by: obtaining flag informationindicating whether the luma intra prediction mode is derived based onintra prediction modes of neighboring blocks of the current block, anddetermining the luma intra prediction mode based on the intra predictionmodes of the neighboring blocks when the flag information indicates thatthe luma intra prediction mode is derived based on the neighboringblocks of the current block.
 8. The apparatus of claim 5, wherein thepredefined value is equal to 4.